DE8710796U1 - Ring-shaped support element for an artificial hip socket - Google Patents

Description

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The invention relates to a carrier element (screw socket) of the type specified in the preamble of claim 1.

With such ring-shaped support elements, which can be screwed into the correspondingly milled acetabulum without the use of a thread cutter thanks to their self-supporting cutting flanks arranged in the form of a thread, the aim is to provide additional protection against unintentional twisting of the cup under load.

For this purpose, it is known in particular according to EP-A2 179 736 to provide at least one opening in an area of the support element that is left free as a cutting groove with surface parts whose surface vector is directed essentially in the | direction of movement of the support flanks when screwing in, thus forming an | additional inhibition when growing into the bone. |

The disadvantage here is that the additional blocking agents are only effective after the socket has grown in.

From the German utility model G 86 83 855.8, a cement-free, self-tightening hip joint socket is also known, which is designed as a closed outer socket (in the form of a surface of rotation of an arc), with incisions extending from the edge of the socket (with the edge lying back in the direction of insertion) so that expandable segments are formed.

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The disadvantage of this design is that the strength of the cup is reduced due to the sharp-edged, pointed insertion cuts. Furthermore, the areas that can only be expanded in the rear part of the cup (when screwing in) mean that, particularly in the case of a flat acetabulum, the expansion process starting from the lower edge of the smooth cup has a tendency to loosen the cup.

JLÖ The invention is therefore based on the object of specifying a support element of the aforementioned type, which makes it possible to create an additional fixation in the area of the annular support element that is brought forward when screwing in, whereby the strength of the pan should essentially be maintained.

This object is achieved with the features specified in the characterising part of claim 1.

In the present invention, it is particularly advantageous that the outwardly spread thread segments in the front part of the support element form an additional anti-twisting device, so that in the screwed-in state after the corresponding segments have been spread out, a reliable anti-twisting device is provided, so that the hip joint prosthesis can be loaded immediately. In particular, the strength of the prosthesis is ensured by suppressing the notch effect at the ends of the incisions *

The improved power transmission in the front area is also beneficial when the acetabulum is damaged.

MB37.dll Sheet 6

The remaining crawling areas must be specifically selected for fastening

The securing of the socket in the screwed-in state is also due to the fact that the bone chips of the spongiosa, which are initially loosely carried along when screwing in - or subsequently inserted - remain in the final position of the socket between the areas provided with threaded support flanks and "grow" there in the rest position of the socket by being incorporated into the newly forming bone tissue at the edge of the socket.

These transversely extending surfaces which block the screw movement form the side surfaces of trough-shaped or other depressions or openings. In the micro range, corresponding surfaces are present in surface roughnesses embedded in the surface or applied to it, known as madreporation. A corresponding effect can also be achieved preferably by plasma spraying titanium material onto the surface of the socket between the thread segments. The combination of two or more of the above-mentioned measures also has a particularly beneficial effect, so that each of the measures can have an effect depending on the individual case, depending on the different conditions encountered when screwing in.

The measures mentioned are particularly advantageous in their application if the doctor

ME37.G11 Sheet 7

Bone chips that accrue during screwing can be filled into the cavities found and compressed there.

If the depressions are designed as openings, the surgeon also has the option of pressing bone chips in from the inside of the socket and compressing the material there by snapping the socket insert into place.

It is also particularly important that if the expansion of the socket is carried out by means of appropriate actuating means immediately during implantation, the primary fixation achieved is very high, whereby the secondary fixation is added to the primary fixation by the growth of bone material in the areas with recesses and is not canceled out again by subsequent expansion of socket parts.

It is therefore not possible, for example, to produce a ring-shaped design of the pan, in particular with incisions extending to both ring edges.

Advantageous further developments of the invention are characterized in the subclaims or are presented in more detail below together with the description of the preferred embodiment of the invention with reference to the figures. They show &igr;

Figure 1 shows a first embodiment of the invention and JO

Figure 2 shows a second embodiment of the invention.

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ME37.G11 Sheet 8

In the carrier element 1 shown in Figure 1, which is ring-shaped and whose outer surface corresponds to the surface of a spherical zone, a number of thread-shaped support flanks 2 are provided, which are separated from one another by cutting grooves 3. The support flanks forming the thread segments are sharp-edged on the parts that are brought forward when screwing in and protrude furthest from the spherical surface here. In the area of the cutting grooves they form sharp-edged tips, which are designated by 4 as an example. In areas that are further back - in relation to the direction of rotation to be used when screwing in - the thread segments are blunted or flattened towards their outer edges, which can be done by parallel machining of the thread segments lying one above the other by means of milling or the like. The ring-shaped carrier element is preferably made of titanium, the elastic properties of which, with a suitable cross-sectional dimension, correspond approximately to those of the surrounding bone material.

A socket insert 5 is adapted to the inner cross-sectional dimensions of the carrier element 1 and can be inserted from below into the carrier element already screwed into the bone, whereby the upper dome-shaped region 6 of the insert projects beyond the carrier element and, when inserted, is supported inside the recess in the bone.

Openings 7 extend - as can be seen in the figure - between the edges of the supporting flanks 4 in the area of the cutting grooves 3 perpendicular to the screwing direction of the

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ME37.G11 Sheet 9

self-tapping support element. The openings pass through the cross-section of the metal support element 1.

The bone chips that accrue during self-tapping screwing are caught in the openings7 and collected there, whereby the preferably steep-flanked side surfaces on the rear edges - seen in the screwing direction - ensure that the chips are safely captured. If the support element is immobilized after screwing in, the bone chips grow on and prevent the cup from being accidentally twisted - and in particular from being unscrewed in an uncontrolled manner - whereby the steep flanks of the edges leading in the screwing direction, in conjunction with the grown bone chips, form an effective barrier.

In the position according to Figure 1, slots 8 are also visible, which extend to the upper edge of the ring-shaped support element (which is guided forward when screwing in) and are directed perpendicularly to the edge of the support element with the larger diameter. The slots open into the pre-rounded openings 7 with an oval cross-section, which run in the meridian direction, with an enlarged diameter and oval shape, which on the one hand prevent cracks from forming due to notch effects and on the other hand there is space here for the growth of bone material or for the insertion of chips, which also facilitates the growth of the socket. The oval (or elliptical) recesses with their larger dimensions also extend in the meridian direction.

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The slots 8 are designed so narrowly that the socket gives way as little as possible towards the inside when screwed in and the opposing side walls of the slots block each other when stresses occur during the thread cutting process. The design of the tapered surface of the support element ensures that it assumes its optimal shape required during the automatic thread cutting when the slots are close to one another.

In the further embodiment of a support ring 1' shown in Figure 2, it is clear how slots 8 ¹ running in the meridian direction alternately extend from the two ring-shaped boundary edges to circular openings 7'. The length of the slots is also selected so that the slots overlap. In this way, a corresponding clamping element for spreading the socket during the course of implantation can ensure that the support ring expands radially evenly - i.e. in both the upper and lower areas. This means that - especially in the case of a spherical socket - the expansion of the socket does not generate a force component that promotes emergence from a flat acetabulum.

In the embodiment shown in Figure 1, the openings 7 are adjoined by roughened zones 9 in the meridian direction, which extend in a vertical direction between the areas provided with thread segments, corresponding to the trough-shaped recesses.

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correspond in width to the openings 7« The madreporation can be either raised or recessed and corresponds in its design to an accumulation of balls of 0/3 to 0/7 mm diameter in convex or concave shape* The bulging of the zone can in another preferred embodiment also be applied by plasma spraying of titanium material or by pino nrvi*öce Coafrnl 1-tinn dot" Clhprf &Igr;&agr;&pgr;&Kgr;&ogr; rlnmh etching _ - _ ... .. j. &mdash;_&mdash; _ -j «.&mdash; _vn . _H &mdash; _ _v .. _....·__.-_...

and the like. The measures are based on the knowledge that when the socket is screwed in, these areas initially cause only a small amount of friction in contact with the surface of the acetabulum - but after some time, when the bone material is connected to the surface of the socket, it adheres firmly in the relevant areas and forms an effective anti-rotation device.

In the embodiment shown in Figure 2, additional recesses 9 ¹ extend along the cutting grooves 3 perpendicular to the screwing direction of the self-tapping support element. The recesses form depressions which do not completely traverse the cross section of the metal support element 1 , so that a hermetic seal between the inside and outside of the pan is still provided and thus in particular the chips produced during the screwing process do not reach the inside of the pan.

The recesses do not directly adjoin the openings 7' and have a width of essentially 3 mm and a depth of 1 to 1.5 mm, with the edges adjacent to the support flanks being formed with steep flanks.

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And the front sides of the recesses merge with a slight gradient into the outer edge of the pan"

The resulting bone chips are caught in the trough-shaped recesses 9 ¹ and collected there, whereby the preferably steep-flanked side surfaces on the rear edges - seen in the screwing direction - ensure that the chips are securely captured. If the support element is immobilized after screwing in, the bone chips grow and prevent the cup from being accidentally twisted - and in particular from being unscrewed in an uncontrolled manner - whereby the sharp flanks of the edges leading in the screwing direction, in conjunction with the grown bone chips, form an effective barrier.

The edges of the depressions 9 ¹ are also steeply formed so that a secure hold against twisting is provided when bone material has grown in. With the openings leading through to the interior, the surgeon has the option of inserting additional bone chips into the openings from the inside of the socket 1, which are compressed during the process of inserting the socket insert 5. The preferred diameter of the openings is 5 mm.

The means for expanding the pan are not shown in detail here. In this respect, reference is made to the application filed at the same time by the same applicant, which shows screwing means that can be operated from the concave side of the pan and which expand the expandable parts by means of a cone, wedge or lever effect.

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MK37.G11 Sheet 13

The invention is not limited in its implementation to the preferred embodiment given above. A number of variants are conceivable, which also make use of the solution presented in fundamentally different designs.

Claims (7)

medical products GmbH D-100Ü Berlin ME37.G11 Ring-shaped support element for an artificial Höft socket A &eegr; s &rgr; r ü c h e 1. An annular support element for an artificial hip socket, which can be screwed into the bone and tapers in the screwing direction, with, in particular, self-tapping, thread-forming support flanks, whereby between the edge of a support flank which is brought forward during screwing /2 ME37.G11 Sheet 2 and the trailing edge of the preceding supporting flank, an area of the support element is left free as a cutting groove and the area has at least one rounded opening,
5 characterized, that an incision '8, 8 ¹ ' is provided, starting from the opening (7, 7') and extending towards the adjacent ring edge, that the incision is directed towards the ring edge with a larger diameter, wherein parts of the support element (1, I ¹ )/ <3ie located in the region of these incisions are provided with thread segments (4) or corresponding projections and can be spread outwards. 2. Support element according to claim 1, characterized in that the incision is directed substantially perpendicular to the adjacent edge. 3. Support element according to one of the preceding claims, characterized in that the incision extends along a cutting groove. 4. Support element according to one of the preceding claims, characterized in that at least it t % ■ I I I I J 11:1 l &bull; * 4 &bull; · · · KlI 1» » i I < · t f ·«* ·· ■ ·· 1» lit ME37.G11 Biätifc 3 at least one incision is provided starting from each circular edge. 5. Support element according to claim 4, characterized in that the indentations extending from both edges overlap one another. I 6. Support element according to one of the preceding claims, characterized in that the openings are circular, ellipsoidal or oval. 7. Support element according to one of the preceding claims, characterized in that an incision, an opening and/or a trough-shaped recessed or madreporated or otherwise roughened area are arranged adjacent to one another. /4